1. Field of the Invention
The present invention relates to a throttle body which controls an amount of air moving toward an engine, and more particularly to a tandem valve type throttle body which is provided with a throttle valve controlled so as to be opened and closed by an accelerator within an intake passage provided in the throttle body, and a sub throttle valve arranged in the intake passage in an upstream side of the throttle valve and operated so as to be opened and closed by an electromagnetic actuator or the like.
2. Description of Prior Art
In accordance with a conventional tandem valve type throttle body, the throttle valve is operated so as to be opened and closed by the accelerator, and the sub throttle valve is operated so as to be closed by the electromagnetic actuator or the like. For example, at a time of traction control or the like, the sub throttle valve is forcibly closed, whereby a torque of the engine is reduced at a time when a slip is generated. Further, in the tandem valve type throttle body, the sub throttle valve is left open at a high opening degree by the electromagnetic actuator, and the throttle valve is forcibly left open toward a first idle opening degree from an idle opening degree in synchronization with the opening motion of the sub throttle valve without relation to an accelerator operation, thereby increasing an air amount moving toward the engine and improving a low temperature starting characteristic of the engine.
In the conventional tandem valve type throttle body mentioned above, the sub throttle valve attached to a sub throttle valve shaft and the throttle valve attached to a throttle valve shaft are structured such that a sub throttle valve lever fixed to and arranged at one end of the sub throttle valve shaft and a throttle valve lever fixed to and arranged at one end of the throttle valve shaft are connected to each other by a transmission member constituted by a link arm, a link lever and the like. Further, a motor corresponding to the electromagnetic actuator driven by an output signal from an ECU is connected to another end of the sub throttle valve shaft via a gear. On the other hand, in the case of employing the transmission member mentioned above, the link arm and the link lever are rotatably connected to respective supporting shafts, whereby a rotation of the sub throttle valve lever is transmitted to the throttle valve lever. Further, a spring member for absorbing a play in the connection portion to one side is engaged with and arranged in the transmission member. The absorption of the play is effective in view of reducing a hysteresis and an abrasion at a time of forward and backward rotating of the transmission member. Further, in the case of arranging the spring member in the transmission member, a spring force of the spring member forms a resistance against driving of the motor, so that it is hard to employ a compact motor in which a generated torque of the motor is small, and in particular, a problem is generated in a structure such as a motor cycle in which a receiving space is limited.